The present invention relates to a cylinder having two piston and rod assemblies and more particularly, a cylinder having three stable positions of the piston and rod assemblies including a fully retracted position, a fully extended position, and a predetermined mid-position.
Pneumatic or hydraulic cylinders are known to be used to move objects with the movement of the associated piston and rod assembly. In most instances, it is desirable to move the object from the position where the piston and rod assembly is fully retracted to the position where the piston and rod assembly is fully extended. In addition, it is sometimes necessary to move the object to a position extension that corresponds with a predetermined mid-position of the piston and rod assembly. In the prior art, to accomplish this, it is necessary to provide a tandem cylinder such that a cap end cylinder has a stroke corresponding to the mid-position extension and the rod end cylinder has a stroke corresponding to the cylinder""s full stroke length. The cap end cylinder then moves the piston and rod assembly to the first mid-point extension before stopping. Pressure applied to the cap end of the rod end cylinder moves the piston and rod assembly the remaining length extension to provide the final displacement. As a result, a tandem cylinder will have a length equal to the length of a cylinder of the full stroke plus the length of a cylinder of the mid-position stroke. This configuration can be a disadvantage where available property around the cylinder and the moveable object is at a premium.
It is the intent of the present invention to address the aforementioned disadvantage. According to the invention, it is desired to provide a three position cylinder with two piston and rod assemblies, wherein the cylinder housing has a length that is less than the total combined stroke lengths of the piston and rod assemblies.
In one aspect of the invention, a three position cylinder assembly is provided for movement between a fully retracted position to a mid-position extension and to a fully extended position. The cylinder assembly has an outer cylinder housing connected between two bases, the first base defines a cap end of the cylinder and the second base defines the head end of the cylinder. The three position cylinder assembly also includes a first piston connected to a first rod and a second piston connected to a second rod wherein both the first and second pistons are disposed within the outer cylinder. The second base has an aperture therethrough to permit extension of the rods beyond the outer cylinder housing. A bumper disposed in the outer cylinder defines a stop means for one of the pistons. The stop means further defines the mid-position extension of the cylinder assembly.
In another aspect of the invention, the three position cylinder assembly further includes a stationary tubular member connected to one end of the outer cylinder and extending a predetermined length within the outer cylinder, and wherein the first piston has reciprocal movement along the outside surface of the tubular member. The tubular member has a stop means on the free end.
In another aspect of the invention, the first rod has an open end distal from the first piston for providing a fluid passageway therethrough and an expanded collar connected to the first piston. The second piston has reciprocal movement along the first rod.
In yet another aspect of the invention, the first piston forms a first fluid chamber on one side and defines a wall for a second fluid chamber on the other side of the first piston. The second piston forms a third fluid chamber on one side of the second piston and defines another wall for the second fluid chamber on the other side of the second piston.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.